ESTRO 2025 - Abstract Book

S4319

RTT - Treatment planning, OAR and target definitions

ESTRO 2025

Conclusion: The ATS-Lite workflow has been successfully integrated as an RTT-led process, with median treatment times under 25 minutes, making 30-minute time slots feasible for long-scheme radiotherapy.

Keywords: Workflow, MR-Linac, Timing

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Digital Poster Implementation of a VMAT technique to treat breast/chest wall cancer patients with level 3 and/or 4 nodal involvement Matthew N Brennan 1 , Anthony Packwood 1 , Alison Dixey 1 , Sydney Marshall 1 , Usman Lula 1 , Sofia Parveen 1 , Eleanor I Woodcock 2 , Sophie Park 1 , Aaliyah Reid 1 , Ellie Golding 1 , Sundus Yahya 2 , Sallie Melsom 2 , Ben Allen 2 , Jenny Sherriff 2 , Daniel Henderson 2 , Andrea Stevens 2 1 Radiotherapy Physics, Queen Elizabeth Hospital, Birmingham, United Kingdom. 2 Radiotherapy, Queen Elizabeth Hospital, Birmingham, United Kingdom Purpose/Objective: The project aimed to safely implement a VMAT approach to replace the current conformal half-beam blocked tangential breast fields with a matched anterior field, with the intention to improve nodal coverage whilst minimising the low radiotherapy dose bath and OAR doses. Material/Methods: Ten anonymised conformal patients were retrospectively replanned with a VMAT technique. The doses delivered to the PTVs, OARs, and low-dose regions were clinically compared with the results favouring the VMAT approach. Subsequently, a pilot study involving twenty patients was initiated. Patients that were eligible for breast/chestwall, plus level 3 and/or 4 nodes, but IMC negative were entered. All patients were CT scanned with a Wingboard, undergoing MVision AI contouring of breast/chest wall, nodal CTVs, and OAR’s which were peer reviewed independently by two consultant clinicians. A dual-arc VMAT technique, with robust optimisation, and short treatment delivery times was employed. Clinical goals established by the FastForward lymphatics and PARABLE trials were used. Recorded planning metrics included doses to PTVs, OARs, CI, HI, and low dose exposure. SGRT was used to manage setup on treatment. Each fraction was assessed to test for plan robustness and evaluated dosimetrically. Results: All treatment plans achieved the clinical objectives for which the conformal plans were designed. The VMAT plans showed a significant improvement in nodal PTV coverage, with an average V36Gy of 89.8% for conformal plans compared to 99.8% for VMAT. Additionally, breast and chest wall PTV coverage improved, with V38Gy values of 96.7% for conformal plans versus 98.9% for VMAT. With the exception of the heart, OAR doses were lower or comparable for VMAT, exhibiting smaller standard deviations. Treatment times were reduced, feedback from treatment staff indicated a preference for VMAT, which was also better tolerated by patients generally, especially those undergoing DIBH. 30Gy and 20Gy dose volumes to normal tissue were reduced using VMAT, but 10Gy and 5Gy dose volumes were higher than the conformal plans, whilst the remaining, clinically acceptable. Data collected from the pilot study facilitated the development of a knowledge-based planning approach for low-dose volume control generating achievable values for future plans. Conclusion: VMAT is a safe and effective technique for non-IMC nodal breast patients. It offers significantly improved coverage of the nodal PTV while minimising any adverse effects on OARs, thereby potentially improving clinical outcomes.